DESCRIPTION (Adapted from the Principal investigator's Abstract): Overall goal of this project is to define the functional consequences of interactions between the protein tyrosine kinase receptor, c-Kit, and its ligand, stem cell factor (SCF) during development of T lymphocytes. The project aims to define the consequences of functional intercellular communication events mediated by c-Kit and SCF that are significant to the biology of organ-specific T lymphocyte development. Specifically, the investigator proposes as follows: 1) to determine the role of thymic stromal-derived stem cell factor in thymocyte and intestinal T-cell development, 2) to determine the role of intestinal epithelial cell-derived stem cell factor in intestinal T-cell development and 3) to determine if stem cell factor and interleukin 7 are redundant or synergistic cytokines for thymic and intestinal T-cell development.